Zootaxa 4350 (1): 121–135 ISSN 1175-5326 (print edition) http://www.mapress.com/j/zt/ Article ZOOTAXA Copyright © 2017 Magnolia Press ISSN 1175-5334 (online edition) https://doi.org/10.11646/zootaxa.4350.1.7 http://zoobank.org/urn:lsid:zoobank.org:pub:1894067C-E4E2-4A64-ACDE-1053E034270F A taxonomic revision of the genus Apostichopus (Holothuroidea: Stichopodidae) from Japan SAU PINN WOO1, 6, AKITO OGAWA2, SHAU HWAI TAN3, 4, ZULFIGAR YASIN3, HIROSHI KAJIHARA1 & TOSHIHIKO FUJITA5 1Department of Natural History Sciences, Graduate School of Science, Hokkaido University, Kita-10 Nishi-8, Kita-ku, Sapporo, 060– 0810 Japan. E-mail:[email protected]; [email protected] 2Graduate School of Science, The University of Tokyo, 7–3–1 Hongo, Bunkyo-ku, Tokyo, 113–8654 Japan. E-mail: [email protected] 3School of Biological Sciences, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia. E-mail: [email protected]; [email protected] 4Centre for Marine & Coastal Studies (CEMACS), Universiti Sains Malaysia, 11800 USM, Penang, Malaysia. E-mail: [email protected] 5Department of Zoology, National Museum of Nature and Science, 4–1–1 Amakubo, Tsukuba, Ibaraki, 305–0005 Japan. E-mail: [email protected] 6 Corresponding author. E-mail: [email protected] Abstract Complete redescriptions of sea cucumbers in the genus Apostichopus Liao, 1980 are provided using the type specimens and specimens deposited in the National Museum of Nature and Science, Tsukuba, Japan. The genus consists of A. arma- tus (Selenka, 1867) and A. japonicus (Selenka, 1867), which can be distinguished by some spicules in the dorsal body wall; the rim of reduced table spicules in A. armatus is spinous, while that in A. japonicus is smooth. Spicules from the tentacles, papillae, tube feet, and cloaca are similar for both species. Key Words: Sea cucumber, Echinodermata, taxonomy, spicules, Apostichopus Introduction The taxonomy of the sea cucumber genus Apostichopus Liao, 1980 has been in flux, and involves four nominal taxa, three colour morphs, and two valid species. The four nominal taxa are: Stichopus japonicus Selenka, 1867, Holothuria armata Selenka, 1867, Stichopus japonicus var. typicus Théel, 1886, and Stichopus roseus Augustin, 1908; all have been established based on specimens from Japanese waters. The three colour morphs (red, green, and black) were first recognized by Mitsukuri (1912) by examining specimens from Japan, Far East Russia, and Korea. Mitsukuri (1912) regarded these colour morphs as representing a single species, to which he applied the name Stichopus japonicus, synonymizing Holothuria armata and S. j. var. typicus. Stichopus roseus, described by Augustin (1908), was not included in Mitsukuri (1912), which was published posthumously by H. Ohshima (Mitsukuri 1912: 2, footnote) after Mitsukuri’s death in 1907. Choe & Ohshima (1961) showed that the green and red morphs might represent different species due to the differences in morphology (Polian vesicles, spicules, and gelatinous layer in mature eggs), spawning and aestivation periods, and preferences for sediment type and salinity. The idea of the presence of the two different biological entities, each represented by the red morph and the green/black morphs, has been supported by allozyme (Kanno & Kijima 2003) and microsatellite (Kanno et al. 2006) data. However, Sun et al. (2010) concluded that all the colour morphs belonged to a single species by showing uncorrected p-distances of CO1 gene sequences between different colour morphs; the maximum value reached 1.48%. On the other hand, Ward et al. (2008) and Uthicke et al. (2009) found that intraspecific variation in CO1 was 0.6–0.72% for holothuroids including Stichopus. Therefore, the genetic distances of CO1 shown by Sun Accepted by M. Eléaume: 27 Sept. 2017; published: 16 Nov. 2017 121 Licensed under a Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0 et al. (2010) is not in contradiction to Kanno & Kijima (2003) and Kanno et al. (2006) who argued the existence of two valid species in Apostichopus. Kuramochi & Naganuma (2010) put an end to this taxonomic suspension by applying the names Apostichopus japonicus (Selenka, 1867) to the red morph and A. armatus (Selenka, 1867) to the green/black forms. However, their figures illustrating the spicules (Kuramochi & Naganuma 2010: figs 2, 3) were of low resolution, without scanning electron microscope (SEM) images showing detailed features that are essential in differentiating the two species. Furthermore, the description provided by Kuramochi & Naganuma (2010) only included spicules from the dorsal body wall and from the tentacles. In this study, a revision of the genus Apostichopus with full description of spicule assemblages from dorsal body, papillae, tentacles, tube feet, and cloacal wall is done by examination of type specimens and additional specimens of Apostichopus using SEM. Materials and methods Sea cucumber specimens of the genus Apostichopus loaned from the Museum of Comparative Zoology, Massachusetts, USA (MCZ) and the National Museum of Nature and Science, Tsukuba, Japan (NSMT) were examined. Spicules were extracted from the tissues of the middle part of dorsal body, papilla tips, tentacles, tube feet, and cloacal wall. The tissues were dissolved using commercial bleach. The spicules were then washed several times with deionized water and absolute alcohol. Extracted spicules were air dried and mounted on SEM stubs. The spicules were coated with gold–palladium alloy and observed under a JEOL JSM-6380LV SEM with the acceleration voltage of 20 kV. Taxonomy Order Aspidochirotida Grube, 1840 Family Stichopodidae Haeckel, 1896 Genus Apostichopus Liao, 1980 Type species. Stichopus japonicus Selenka, 1867 (but see Remarks below). Type locality. Japan Diagnosis. Mouth ventral, surrounded by twenty peltate-shaped tentacles. Body stout and cylindrical. Conical papillae conspicuous or less conspicuous, protruding at dorsal and lateral sides of body; similar conical papillae arranged in one line at ventro-lateral sides; smaller papillae scattered on dorsal and lateral surfaces. Background body colour highly variable from red to brown and green to black. Gonads in two tufts. Spicules taking form of tables, buttons, multiperforated plates, rods, and complex plates. Dorsal body-wall spicules composed of tables; often reduced with pillars absent, but simple and not spinous if present; rims smooth or spinous. Dorsal body wall of juvenile contains tables with four spires, each having multiple spines on its end, with two to three crossbeams. Rosette and C-shaped spicules absent in dorsal body wall of both adult and juveniles. Papillae containing elongated buttons, rods, tables, and multiperforated plates. Rods in tentacles. Ventral tube feet containing multiperforated plates and tables, the latter without pillars. Spinous complex plates present in cloacal walls both in adult and juvenile. Species composition. Apostichopus armatus (Selenka, 1867); Apostichopus japonicus (Selenka, 1867) (see Remarks). Remarks. Liao (1980) erected this genus based on material from the northern East China Sea that was identified as Apostichopus japonicus. Judging from the drawings of the spicules, Liao’s (1980) material was most likely to represent Apostichopus armatus (Liao 1980: fig. 1), to which Article 70.3 (Misidentified type species) of the Code (International Commission on Zoological Nomenclature 1999) applies. In order to serve stability and universality of the name, we take the option stipulated under Article 70.3.1, in which the nominal species previously cited as the type species is to be retained, because alteration of the type species will not affect the genus name usage. The diagnosis for Apostichopus given by Liao (1980) sufficiently illustrated clear separation of Apostichopus from other genera based on reduced table spicules without pillars in the body wall (Liao 1980: fig. 1). 122 · Zootaxa 4350 (1) © 2017 Magnolia Press WOO ET AL. The absence of C-shaped spicules and the presence of reduced table spicules in the dorsal body of Apostichopus differentiate it from the genera Stichopus and Isostichopus Deichmann, 1958, which have abundant C-shaped spicules and no reduced table in the dorsal body (Clark 1922; Deichmann 1958). The genus Apostichopus also can be easily distinguished from the genera Thelenota Brandt, 1835 and Astichopus Clark, 1922 by the presence of table spicules that are absent in the dorsal body of the two genera (Clark 1922). Complex plates in the cloacal walls and elongated buttons in the papillae are observed in Apostichopus (Théel 1886; Liao 1980) and Parastichopus Clark, 1922 (Clark 1922; Lambert 1986). The well-developed table spicules with complete spires in the dorsal body of Parastichopus are absent in adult Apostichopus (body length greater than 70 mm) (Mitsukuri 1897). Furthermore, Apostichopus can be found from the intertidal zone to the depth of about 20‒40 m (Zhao 2015), while Parastichopus is distributed only in deeper waters from 30 m down to the depth of 600 m (Deichmann 1937; Lambert 1986; Imaoka et al. 1990). We only included two species in the species list of Apostichopus. This is contrary to the inclusion of Parastichopus californicus (Stimpson, 1857), Stichopus johnsoni Théel 1886, Parastichopus leukhothele Lambert, 1986, Parastichopus multidentis Imaoka, 1991, Stichopus nigripunctatus Augustin, 1908, Parastichopus nipponensis Imaoka, 1990 (synonym of P. nigripunctatus) and Stichopus parvimensis Clark, 1913 by Paulay (2013) as part of the